Discussion of the Background
Aluminum-polyethylene composite laminates, as well as other types of composite laminates, are useful for a number of architectural applications, because the laminates combine light weight with high strength. These laminates may be used as finished surfaces or for all or portions of the interior or exterior surfaces of a building or an automobile.
In the field of composite material manufacturing, a lamination machine is used to produce a composite material consisting of, for example, a layer of polyethylene sandwiched between layers of sheet aluminum. U.S. Pat. No. 4,994,130 to Ichikawa et al. teaches a lamination machine which includes pay off reels 3 and 3' that are used to feed the sheet aluminum to preheaters 6 and 6', then to hot press bonding rollers 2 and 2' where a synthetic resin sheet is pressed between the aluminum sheets, and thereby bonded to the aluminum sheets with a thermally activated adhesive. The lamination machine typically uses large rolls of sheet aluminum and extruded polyethylene to form long continuous sheets of composite material. In order to ensure a uniform or complete distribution of polyethylene between the aluminum sheets, it is common to extrude the polyethylene so that it is slightly wider than the aluminum sheet rolls. Therefore the composite laminate leaving the laminating machine will typically have a small amount of polyethylene projecting from the edge of the material. In order to ensure that the edge of the final product is flush, the longitudinal edge of the sheet is trimmed off as it leaves the lamination machine, and the trimmed laminate is then cut laterally to form panels. The continuous longitudinal trimming the edge of the laminate results in large amounts of trim material, that heretofore have been wasted.
Since the materials which form composite materials, such as aluminum-resin composites, can be expensive, particularly in large volumes, it is desirable to recycle both the metal and the resin components. In the past, panels or sheets of such composite materials have been recycled. In recycling such sheets, for example, when the metal sheets include aluminum, it is important to separate the aluminum from the thermoplastic resin prior to melting the thermoplastic resin, since melting of the aluminum-thermoplastic resin leads to conversion of the aluminum to aluminum oxides and a poor yield of recovered aluminum. It is known to separate aluminum polyethylene laminate composite utilizing a two stage process, in which the laminate is first heated and then pressed between picking rolls. See U.S. Pat. No. 5,500,072 to Fujimura et al. col. 1, lines 58-67. However, this method is not effective when the aluminum sheet is relatively thick or is composed of less pure and less flexible aluminum. Furthermore, it has been found that heating the laminate for separating requires a large amount of energy, and is not conducive to a continuous separating process.
U.S. Pat. No. 5,500,072 to Fujimura et al. teaches a method and apparatus for separating aluminum sheets from thermoplastic resins that are cut into panels. Fujimura et al. teach a method and apparatus which includes feeding the cut laminate through embossing rollers, then through a heating zone. When the material emerges, "it separates spontaneously into its component metal sheets 4 and resin core 3 upon cooling." See Fujimura et al. at column 6, lines 4-6. However, a process which requires heat consumes a substantial amount of energy, and is therefore costly, and contrary to the purpose and desirability of recycling, particularly with a relatively small width trim (e.g., trim separated from the longitudinal edges of a laminate).
U.S. Pat. No. 5,194,109 issued to Yamada teaches a method for recovering scraps of a multilayer plastic sheet or film. With the Yamada method, the scrap is heated to a temperature lower than the softening point of the base material layer so that the inter-laminar peeling strength of the adhesive resin is lower than the strength of the weakest layer in the lamination, and the multilayer scrap is separated into at least two scrap layers. Yamada utilizes heating rolls, a pair of separation rolls downstream from the heating rolls, and rollers which are used to take-up the outer layers of the heated and separated laminate. Yamada also teaches that heating can be performed by hot air or infrared rays. See column 4, lines 61-63. However, this method also suffers from the high energy requirements of heating the laminate trim.
Thus there remains a need for a method and apparatus for separating sheet metal-thermoplastic resin laminate trim composites into their component metal sheets and thermoplastic resin sheets.